[llvm] [RISCV] Emit VP strided loads/stores in RISCVGatherScatterLowering (PR #98111)

[Luke Lau via llvm-commits]

lukel97 wrote:

Rebased and updated to remove `riscv_masked_strided_{load,store}` now that the last user is gone

https://github.com/llvm/llvm-project/pull/98111